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Is less torque generated (produced) by your upper arms (forearms and arms) when there is no space between you and the ground (ie when you are lying completely flat on your stomach and you are trying to forcefully push off the ground). Is there a handicap torque-wise because: 1) there is absolutely no space between your body and the ground? 2) you are then not able to place your upper arms in the ideal position to produce the best torque possible? 3) your forearms are completely flexed on your arms? Or is my impression that a minimal space is required, physic wise, between your body and the ground to generate the best torque possible is just an impression? Thank you for your insights and your time.

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Torque needs to be measured relative to an axis, so let's assume the axis is a line parallel to the ground, perpendicular to the body's long axis, and going through the person's toes. That way the force exerted by the ground on the toes does not produce a torque.

In this case, the torque is equal to the distance from the axis (toes) to the hands' point of contact at the ground, times the vertical component of the force exerted by the hands. In your scenario the distance from axis to hands does not change, so all that changes is the vertical component of the force exerted by the hands.

If you do the math, you will find that the torque goes as $cos(\alpha)$, where $\alpha$ is the angle measured up from the ground: the angle between the body's long axis and the line from toes to hands. This means the torque is maximum when the body's long axis is horizontal.

Without needing to do the math, you know that if the body is vertical, no (hand) force is needed to keep it from tipping over, so there is no vertical component of the force. If the body is horizontal, the (hand) force needed to hold it stationary is maximum.

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  • $\begingroup$ Thank you very much. $\endgroup$ Jun 1, 2019 at 13:38
  • $\begingroup$ I realize that force and torque are not exactly the same. If the word "force" had been used instead of "torque", would your answer be the same? I am interested in human body mechanics. Thank you $\endgroup$ Jun 1, 2019 at 13:43
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Yes the more acute the angle of the elbow joint the less torque the arm muscles have on the bones. See how hard you can push, or pull, with your elbow fully folded [acute angle] now see how much easier it is to exert the same force with the elbow past a 90 degree angle.

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